Preparation of chalcogenide glass sputtering targets

ABSTRACT

A method of preparing large area chalcogenide glass sputtering targets. These targets are prepared in an evacuated chamber or inert gas atmosphere by heating a boule of chalcogenide in a quartz dish to contour the bottom face of the target. While heating the boule, a weight forces a wire mesh with a stud attached into the top surface of the boule. After a predetermined time to insure good physical bond between glass and mesh, the chamber is cooled to ambient and the sputtering target (chalcogenide glass-mesh-stud) may be removed.

United States Patent 1191 1111 3,850,604

Klein Nov. 26, 1974 15 PREPARATION OF CHALCOGENIDE 2,733,501 2/1956Orthuber et a1. 29/2517 3,228,104 1/1966 Emeis GLASS SPUTTERING TARGETS3,310,392 3/1967 Rhodes [75] Inventor: Richard M. Klein, Frammgham, 3,44, 05 9/1969 Landron, Jr, Mass. 3,516,133 6/1970 Smith et a1 g ee GLaboratories Incorporated, 3,714,706 2/1973 Rerzman et a1. 65/59 X W l hM FOREIGN PATENTS OR APPLICATIONS Oct. Germany 1 [21] Appl. No.: 406,066Primary ExaminerS. Leon Bashore Assistant Examiner-Frank W. Miga,Related U'S' Apphcauon Attorney, Agent, or Firm-Irving M. Kriegsman[62] DIVISIOI'I of Ser. No. 313,740, Dec. 11, 1972, Pat. No.

57 ABSTRACT 521 11.5. CI 65/32, 29125.17, 29/25.18, A method ofPreparing large area chalcogenide glass 29/630 65/45, 65/49 65/59,264/272, 264/274 sputtering targets. These targets are prepared in an 511111. c1 C03c 29/00 H01 j 9/00 evacuated Chamberormertgas atmosphere byheating 58 Field of Search (as/1310.6 32 59 45 a boule of Chalcogenide aquartz dish to Contour the 65/49 54; 29/2517 251 630. 2 4/2 72 274tbottom face 0f the target. heating the b01116, a

weight forces a wire mesh with a stud attached into [56] ReferencesCited the top surface of the b0u1e. After a predetermined time to insuregood physical bond between glass and UMTED STATES PATENTS mesh, thechamber is cooled to ambient and the sputg g z 65/59 X tering target(chalcogenide glass-mesh-stud) may be r ogas 2,196,109 4/1940 Eastusremoved 2,317,754 4/1943 8 Claims, 2 Drawing Figures PREPARATION OFCHALCOGENIDE GLASS SPUTTERING TARGETS This is a division of applicationSer. No. 313,740, filed Dec. 11, 1972, now U.S. Pat. No. 3,791,995.

BACKGROUND OF THE INVENTION tion by placing a boule of chalcogenideglass in a quartz mould to contour the bottom face of the target. Apiece of metal mesh approximately thesame area desired for the target,with a cathode connector or stud attached,

The present invention relates to the field of sputtering targets and,more particularly, to large area chalcogenide glass targets withimproved physical properties and methods for making same.

Chalcogenide glasses, including those materials commonly calledamorphous semiconductors, are being widely investigated for their usefuloptical and electrical properties. Many of the potential applications ofthese materials, including optical and electrical switches, require thatthe glass be in the form of a thin film. Since it has been found thatevaporation techniques are generally not suitable for chalcogenideglasses due to selective evaporation of some of the atomic constituentsof the glass, sputtering has gained wide favor as the thin filmdeposition technique. It is known, however, that in order to obtainuniform thin films over a given area, the area of the sputtering targetused to produce this film must be several times larger.

There are two general techniquesfor preparing chalcogenide glasssputtering targets: fused targets, which are formed by melting the glassin a suitably shaped quartz container; and hot-pressed targets, formedby powdering some fired glass and then hot-pressing the powder into asuitable shape.

One of the disadvantages of fused targets is that a large amount ofglass is required to produce a target of suitable mechanical strength.The strength of the target is important not only during handling butalso during sputtering since these glasses generally soften at lowtemperatures and are prone to thermal shock. In addition, a fused targetis difficult to fasten to the sputtering system cathode. Finally, firingthe glass so as to provide a large area target generally leads to poorglass homogeneity.

Hot-pressed targets, on the other hand. require additional' procedures,i.e., grinding and. hot-pressing, which could affect the purity andchemical composition of the glass. For example, hot-pressing could alterthe composition by means of selective volatilization of the constituentelements. A final disadvantage is that selective sputtering, i.e theremoval'of some constituents of the glass at a faster rate than others,is found to be more prevalent with hot-pressed as opposed to fusedtargets. This leads to inhomogeneous films.

For both types of target mentioned above, the heat generated duringsputtering can easily soften the target and destroy it due to the lowsoftening point of most chalcogenide glass. It is therefore the purposeof this invention to provide a method of producing chalcogenide glasssputtering targets of large area with improved physical properties.

SUMMARY OF THE INVENTION In accordance with the features of the presentinvention. a sputtering target constructed of chalcogenide glass, wiremesh, and cathode connector is prepared by heating the components in acontrolled atmosphere to soften the glass while forcing the wire meshwith a cathode connector attached into the softened glass. The targetmay be prepared according to the present invenis placed on top of theglass. An inert meta] weight is placed over the stud; this weight servesto protect the threads of the studs as well as assure the penetration ofthe mesh into the molten chalcogenide glass. The entire assembly is thenplaced in a quartz ampoule which is evacuated and flame sealed. Theampoule is then heated above the softening point of the chalcogenideglass and held at that temperature for sufficient time to insure goodphysical bond between the glass and mesh. After cooling slowly to roomtemperature the ampoule is opened and the sputtering target(chalcogenide glassmesh-stud) can be easily removed from the rest of theapparatus.

In general, this process provides the advantages of a fused target withregard to uniform sputtering while maintaining the flexibility of thehot-pressed target technique in obtaining large area targets. Inparticular, the advantages are: a large area, mechanically strong targetcan be fabricated using a minimum amount of chalcogenide glass; thesurface of the target is fused; volatilization losses from the glass areminimized by preparing the target in a closed system; the target caneasily be mated to the sputtering system; during sputtering, the metalmesh assists in conducting heat from the chalcogenide glass, thuslimiting its temperature;

and even if the glass does soften during sputtering, it would tend toremain in position due to surface tension so that the deposition wouldnot have to be interrupted.

Further features and advantages of the invention will become morereadily apparent from the following detailed description of a specificembodiment of the invention when taken in conjunction with theaccompanying drawings. In the several figures, like reference numeralsidentify like elements.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic view of an apparatusfor making sputtering targets in accordance with the present invention;and

FIG. 2 is'a perspective view with parts broken away of a sputteringtarget prepared by the apparatus-shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Attention is directed to FIG. I,whereinthe apparatus for producing a sputtering target in accordancewith the present invention is illustrated. A quantity of bulk glass orboule 10 is placed on a mould or dish 12. The

glass may be of any type of chalcogenide useful in sputtering, by way ofexample, one may use 24 atomic percent arsenic (As), l6 atomic percentantimony (Sb), and 60 atomic percent selenium (Se). Any glass shapecould be used depending on the desired diameter and thickness of thefinished target. Bulk glass is preferred to powder or smaller chunks dueto the reduced chance of bubble entrapment in the former. The boule maybe prepared using standard techniques and may be sliced intoapproximately 50 mil thick slices. Thinner slices could be useddepending on the amount of glass available and the desired finishedtarget area as previously mentioned.

The mould or dish may be constructed of any material, preferably havinga much lower coefficient of thermal expansion than the chalcogenideglass, such as quartz. The lower coefficient of thermal expansion allowsthe finished sputtering target to separate readily from the mould.

On top of the boule is placed a reticulated member or mesh which hasapproximately the same area as the desired target. The mesh may beconstructed of any inert material which can withstand the temperatures.used in target preparation. Preferably, a refractory material such asmolybdenum may be used to reduce the chance of metallic diffusion intothe glass because a good physical rather than a chemical bond isdesirable. A cathode connector or stud 16 is fixedly attached to mesh15. The stud may be attached by spot welding and be threaded to mateeasily to a cathode of a sputtering device.

Aninert weight 17 is removably mounted on top of the stud 16. If thestud is threaded the weight may be screwed into place thereby serving adual purpose: 1) to provide sufficient downward force during the targetpreparation to assure the mesh penetration of the molten glass; and 2)to protect the threads on the stud. Therefore, the mass of the weight 17depends on the viscosity of the glass to insure proper penetration ofmesh 15 into the glass 10.

The entire assembly during preparation of the target is enclosed in acontainer a ampoule 20 to control the atmosphere surrounding theassembly either by introducing inert gas into the container orevacuating the container. In either case, the ampoule is sealed by flameor bakeable vacuum seal 21 around the perimeter of container 10. Thecontainer is then evacuated by a conventional technique such as bydiffusion pump (not shown). The container may then be sealed eitherunder vacuum or with backfill of inert gas. The sealing is accomplishedby flame working the exhaust turbulation 25. A vacuum furnace may beused in lieu of ampoule 20. v

The sealed ampoule 20 is heated in a furnace (not shown) to atemperature above the softening point of the chalcogenide glass and leftat that temperature for sufficient time to insure a good physical bondbetween the glass 10 and the mesh 15. The temperature should be chosenfor the particular glass and weight used so that there is some, but notexcessive, penetration of the mesh into the glass. For the 24/16/60As-Sb-Se glass system previously mentioned with a weight of 9.6 grams afiring temperature of 400C was used. Preferably, heating should becontrolled so that there is a temperature gradient vertically down theampoule such that the highest temperatures are at the top of theampoule; in this way volatization losses from the glass are minimized.

After heating, the ampoule is cooled slowly to ambient conditions, therate of cooling should be controlled to reduce strain and avoid failureby thermal shock. After cooling, the ampoule is opened and the target(chalcogenide glass-mesh-stud) illustrated in FIG. 2, can be easilyremoved from the rest of the assembly.

Attention is now directed to FIG. 2 wherein is illustrated a sputteringtarget prepared by the method described hereinbefore. The sputteringtarget is generally numerically designated 30. The target 30 comprises astud 16, mesh 15 and glass 10. The stud 16 is threaded for mating to thesputtering system cathode and is spot welded to mesh 15 which isembedded in the chalcogenide glass 10.

The target may then be mated and used in a sputtering system cathode. Byway of example, in operation of a typical sputtering system, when aninert gas, and, possibly a specific reactive gas, is introduced in thesystem,

' an RF discharge can be initiated between the electrodes. (An RF ratherthan DC discharge is used since the target is non-metallic.) Bombardmentof the target by gas ions accelerated by the high voltage causes particles of atomic dimensions to be ejected from the target. Generally, adark space shield is placed around the tar get to confine the plasma sothat ejected particles are directed toward the anode which comprises thesubstrate for the film being deposited.

Due to the nature of the sputtering process, some of the ion impactenergy dissipated at the target is converted into heat. This heating isparticularly damaging in chalcogenide glasses due to their high thermalexpansion coefficients and low softening points. Targets produced by theaforementioned process are less susceptible to these problems. Firstly,targets can be made thinner to reduce thermal shock failure because ofthe added mechanical stability provided by the metal mesh.

Secondly, the metal mesh assists in conducting heat from thechalcogenide glass, thus limiting its temperature during sputtering.Finally, even if the glass softens slightly during sputtering, the metalmesh will tend to hold the glass in shape.

Another consequence of the sputtering process is that due to thedirectionality of the ejected particles, deposition will only be uniformon the central portion ofthe substrate. This limited uniform area,approximately one-fourth the area of the target, necessitates the use oflarge targets in order to obtain uniformly thick films over asubstantial substrate area. Therefore, another advantage of theaforementioned process is that it facilitates the production of largetargets.

The various features and advantages of the invention are thought to beclear from the foregoing description. Various other features andadvantages not specifically enumerated will undoubtedly occur to thoseversed in the art, as likewise will many variations and modifications ofthe preferred embodiment illustrated, all of which may be achievedwithout departing from the spirit and scope of the invention as definedby the following claims.

What is claimed is:

1. A method of making a chalcogenide sputtering target comprising thesteps of:

a. placing chalcogenide glass in a mould;

b. placing a flat inert mesh with a connector fixedly attached on top ofsaid glass;

c. placing a removable inert weight on said connector for forcing saidmesh into said glass when said glass is heated;

d. heating said glass to a temperature above the softening point of saidglass for a predetermined amount of time to insure a good physical bondbetween said glass and said mesh; and

e. slowly cooling said glass to ambient conditions.

2. The method in accordance with claim 1 wherein the mould is a polishedquartz dish.

3. The method in accordance with claim 1 wherein a boule of chalcogenideglass is used in step a.

4. The method in accordance with claim 3 wherein said chalcogenide glasscomprises 24 atomic percent 7. The method in accordance with claim 6wherein the heating of said glass is performed in a vacuum.

8. The method in accordance with claim 6 wherein the heating of saidglass is performed in an inert gas atmosphere.

1. AMETHOD OF MAKING A CHALCOGENIDE SPUTTERING TARGET COMPRISING THESTEPS OF: A. PLACING CHALCOGENIDE GLASS IN A MOULD; B. PLACING A FLATINERT MESH WITH A CONNECTOR FIXEDLY ATTACHED ON TOP OF SAID GLASS; C.PLACING A REMOVABLE INERT EIWEIGHT ON SAID CONNECTOR FOR
 2. The methodin accordance with claim 1 wherein the mould is a polished quartz dish.3. The method in accordance with claim 1 wherein a boule of chalcogenideglass is used in step a.
 4. The method in accordance with claim 3wherein said chalcogenide glass comprises 24 atomic percent arsenic, 16atomic percent antimony and 60 atomic percent selenium.
 5. The method inaccordance with claim 4 wherein said temperature is 400*C.
 6. The methodin accordance with claim 1 wherein the heating of said glass isperformed in a controlled environment.
 7. The method in accordance withclaim 6 wherein the heating of said glass is performed in a vacuum. 8.The method in accordance with claim 6 wherein the heating of said glassis performed in an inert gas atmosphere.